8.9 Foetal Physiology Flashcards
What is a foetus
A foetus comes in development after the embryo from the beginning of the 9th week of intrauterine life to full term birth. In a foetus, most organs are in place however some may be non functional and still have some growing to do.
What are the two ways foetal growth can be regulated
foetally and maternally
What are some maternal regulations of foetal growth
health of mother, nutrition of mother, genetics of mother, lifestyle of mother
What are some foetal regulations of foetal growth
sex, genetics, insulin like growth factors
Why is it important not to have abnormal foetal growth rates
A high or low birth weight is associated with neonatal mortality
How does foetal growth occur
Foetal growth occurs through hyperplasia (increase in the number of cells) which is mostly controlled by genetic and environmental factors
What are the functions of the placenta
-performs the functions of lungs for gas exchange
-performs the functions of GI tract for nutrition
-performs the functions of the liver for nutrition and waste removal
-performs the functions of the kidneys for fluid and electrolyte balance and waste removal
-is involved in hormone synthesis
The placenta grows as the foetus grows
Describe the heart in the foetus
The heart is the first functional organ to develop in the foetus and the heart beat is initiated at day 21. The foetal heart beat is an important diagnostic tool as congenital heart defects are responsible for half of the birth defect deaths
Describe the foetal circulation
The placenta acts as the lungs to provide gas exchange as the foetal lungs are inactivated. 2 umbilical arteries branch from the biforcated aorta and take blood (some oxygenated and some deoxygenated) from the foetus aorta to the placenta. An umbilical vein carries oxygenated blood back from the placenta to the inferior vena cava. The inferior vena cava collects deoxygenated blood from the lower part of body and oxygenated blood from the umbilical vein. The foramen ovale in the heart opens to allows blood to flow from right atrium to left atrium (allowing blood to bypass lungs) then out of left ventricle into aorta. A little bit of blood is sent to the lungs from the pulmonary artery to provide the developing tissue nutrients. The ductus arteriosus is a branch from the pulmonary artery that delivers any blood sent to lungs back to the aorta.
Describe the oxygen tension between the placenta and foetus
Oxygen moves from an area of high partial pressure to an area of low partial pressure. The umbilical vein has a high partial pressure of oxygen and the umbilical artery has a low partial pressure of oxygen. This allows oxygen to move from the placenta to the foetus.
-foetus also has high haematocrit (ratio of hb to RBC) and a high heart rate to enable sufficient oxygen supply
Describe the difference in saturation curves between foetal haemoglobin and adult haemoglobin
Foetal hb has a higher affinity for oxygen, so at a lower partial pressure of oxygen, foetal haemoglobin will bind to more oxygen than adult haemoglobin.
What is the difference between foetal haemoglobin and adult haemoglobin that gives the foetal haemoglobin a higher affinity for oxygen
In adult hb there are 2 a and 2 b globin chain subunits but in foetal hb there are 2 a and 2 y globin chain subunits.
Describe how a baby switches from placental gas exchange to lung gas exchange at birth
At birth, the umbilical cord is stretched, causing blood vessels from the placenta to restrict and prevent blood flow into the baby. This central acidosis which stimulates respiratory control centres to trigger the first inspiration and stretching of the lungs. So the lungs expand and blood is drawn into the lungs due to the pulmonary vascular resistance in the lungs dropping. This then increases the pressure in the left atrium as blood is returned to the heart from the lungs. This pressure change in the left atrium then causes the foramen ovale to close over.
What is the importance of lung surfactant
It reduces surface tension to overcome the initial negative pressure of air entering the lungs for the first time (and subsequently)
How can a first breath be induced
via tactile stimulation or decreased temperature
